This invention relates generally to radio frequency or microwave circuits, and specifically to techniques for improving the direct current (DC) biasing of oscillators, amplifiers, and other RF/Microwave devices; for improving the gate return for a field effect transistor used in an oscillator; for providing a cavity or enclosure for a dielectric resonator that provides improved temperature stability over a wide frequency range; for providing an improved microwave oscillator; and for providing an improved dielectric resonator tuning device.
Frequency-Adjustable DC Biasing Circuit
Dielectric resonator oscillators (DROs) are very popular devices in the radio frequency (RF) or microwave electronic field. These oscillators are typically employed in communication systems, radar systems, navigation systems and other signal receiving and/or transmitting systems. Their popularity has been attributed to their high-Q, low loss, and conveniently sized devices for various applications in the RF and microwave fields. For the purpose of this application, the terms xe2x80x9cradio frequencyxe2x80x9d, xe2x80x9cRFxe2x80x9d and xe2x80x9cmicrowavexe2x80x9d are interchangeable, and are used to refer to the field of electronics that involve signal processing of electromagnetic energy cycling at a frequency range of about 800 MHz to about 300 GHz.
Although DROs provide substantial advantages over other types of oscillator designs, improving their performance and characteristics is an ongoing process. For instance, some ongoing developments include reducing the size of the DROs, increasing its efficiency, improving its manufacturing and reliability, reducing its phase noise, and improving its temperature stability. Of particular interest to this invention is the latter three objectives.
Manufacturers of DROs are concerned with improving the manufacturing and reliability of their products. The design of DROs presents a particular problem in that DROs typically perform well only for an RF energy or signal cycling at a discreet frequency or within a narrow frequency range. In other words, they generally meet their specified performance only for a very narrow frequency range. It follows then that if a DRO manufacturer wants to produce a line of DROs with different discreet output frequencies covering a wide frequency range, each DRO must be custom tailored for each of the frequencies. This custom tailoring of DROs leads to increased engineering time, manufacturing time, cost, inventory and logistics, and a reduction in the reliability of the DROs.
To illustrate the manufacturing and reliability problem of customizing DROs, consider the typical prior art series feedback or reflective type DRO 10 shown in FIG. 1. The DRO 10 consists of a dielectric resonator (DR) 12, field effect transistor (FET) 14, a DR-coupling or input resonator transmission line 16, output and source impedance matching circuits 18 and 20, direct current (DC) biasing circuits 22 and 24 for the drain and source of the FET, and a FET gate return resistor R3.
In the prior art, the DRO 10 is typically designed for efficiently and optimally producing an RF energy or signal cycling at one specific frequency, or within a very narrow frequency range. For example, the DRO 10 is specifically designed to produce an RF energy or signal cycling at a frequency f0. In order for the DRO 10 to optimally perform, each of the elements of the DRO is tailored designed to optimally operate at such frequency f0. For instance, the dielectric resonator 12 is chosen such that its lowest resonating frequency is slightly below the frequency f0. Similarly, the output and source impedance matching circuits 18 and 20 are designed to provide the optimal impedance matching at frequency f0. Also, the drain and source DC biasing circuits 22 and 24 are designed so that they optimally block an RF energy or signal cycling at the operating frequency of the DRO f0.
To further illustrate the need for optimally designing each of the elements of the DRO 10 for its operating frequency f0, consider for example the drain and source DC biasing circuits 22 and 24. The object of these circuits is to transmit DC power to the FET 14 without affecting the RF energy produced by the DRO 10. To accomplish this objective, the source and drain DC biasing circuits 22 and 24 include respective high impedance transmission lines 26 and 28, each having one end (RF end) connected to an RF-carrying portion of the DRO 10, and another end (DC end) being RF shunted to ground by a bypass capacitor, such as capacitors C1 and C2.
In order for the DC biasing circuits to optimally not affect the RF energy or signal produced by the DRO 10, the length of the high impedance transmission lines 26 and 28 are designed to have a length of a quarter wavelength of an RF energy cycling at the operating frequency of the DRO f0. In addition, the bypass capacitors C1 and C2 are designed to produce an impedance to ground of less than one to two Ohms at the frequency f0. The biasing circuits 22 and 24 typically include resistors R1 and R2 for setting the proper bias voltage for the FET 14. Any deviation of the length of the high impedance transmission lines 26 and 28 from a quarter wavelength length at the operating frequency f0 of the DRO 10 will cause degradation in the performance of the DRO, such as a degradation in the phase noise performance of the device.
From the discussion above, it can be seen that in the prior art DRO 10, the elements of the DRO 10 are tailored designed for optimally operating at the specific operating frequency f0 of the DRO. This presents a problem for manufactures of DROs that need to produce a line of DROs operating at a plurality of different discreet frequencies covering a wide frequency range. In other words, because each type of DROs must be custom designed, it leads to increased engineering time, manufacturing time, cost, inventory and logistics, and a reduction in the reliability of the DROs. Thus, there is a need for a universal DRO design that can be easily modified to optimally operate at a plurality of different discreet frequencies covering a wide frequency range.
Improved FET Gate Return Circuit
Another concern in the design of DROs is the phase noise performance of the device. Reduction in phase noise is desired since high phase noise may affect the performance of systems employing DROs. For instance, DROs often produce an RF carrier that is to be modulated with a baseband signal. If the frequency response of the baseband signal include a relatively low frequency response, its frequency components lie near the RF carrier. If the RF carrier has poor phase noise characteristics, then it will interfere with the modulated baseband signal. Thus, it is desired to reduce phase noise as much as possible in DROs to avoid this interference problem.
Referring again to FIG. 1, one particular element of the prior art DRO 10, namely the FET gate return resistor R3, can cause significant degradation in the phase noise performance of the DRO. The gate return resistor R3 is typically connected in a series feedback or reflective type DRO at the end of the DR-coupling or input resonator transmission line 16. The purpose of the gate return resistor R3 is to provide a path to ground for positive charges that accumulate on the gate of the FET 14 during its operation.
More specifically, during the operation of the DRO 10, a large signal amplitude is generated at the gate input of the FET 14. As the large signal amplitude varies over the positive half of the sinusoid wave, a small amount of positive charges pass through the Schottky diode junction of the gate. These charges interfere with operation of the DRO, and therefore, need to be removed. Thus, the FET gate resistor R3 provides a path to ground to eliminate such unwanted charges. In order to eliminate any unwanted RF reflections off the FET gate resistor R3, this resistor is designed to match the characteristic impedance of the DR-coupling or resonator transmission line 16, which is typically 50 Ohms.
Although the problem of the unwanted positive charges at the input of the DRO 10 is substantially reduced by the FET gate resistor R3, this resistor has an adverse effect of degrading the phase noise performance of the DRO. The reasons for this is that the resistance value of the resistor R3 is relatively low, e.g. 50 Ohms, and it is not properly RF isolated from the DRO circuitry, i.e., it is directly connected to the end of the DR-coupling or resonator transmission line 16. As a result, the resistor affects the RF energy propagating via that DR-coupling or resonator transmission line 16, and consequently, adversely affects the phase noise of the DRO. Accordingly, there is a need to provide a FET gate return resistor that provides a path to ground for the unwanted positive charges emanating from the FET 14, without significantly degrading the phase noise performance of the DRO.
Dielectric Resonator Cavity
Yet another concern in the design of DROs is the temperature stability of the device. Although DROs have superior performance when it comes to phase noise and efficiency, DROs are susceptible to environment temperature changes if they are not properly designed. Therefore, a great deal of engineering time is spent in designing temperature-compensating elements and/or techniques for DROs.
For instance, in FIG. 2, a prior art temperature-compensating DRO circuit 30 is shown. The circuit 30 includes a DRO, such as like the prior art DRO 10 of FIG. 1, coupled to a phase lock loop (PLL) circuit 32. The PLL circuit 32 includes a crystal oscillator 34, a sampling phase detector 36 and a loop filter 38. As it is conventionally known, the crystal oscillator 34 produces a highly temperature-stable sinusoidal signal with typically a much lower frequency fx than the frequency f0 of the DRO output. This sinusoidal signal is coupled to a first input of the sampling phase detector 36, whereas the output sinusoidal signal of the DRO 10 is coupled to a second input of the sampling phase detector 36 by way of a directional coupler 40. The sampling phase detector 36 produces a phase error signal which is coupled to a frequency-responsive component (not shown), such as a varactor, of the DRO 10 by way of a loop filter 38.
Since the output of the crystal oscillator 34 is highly temperature stable, the output of the DRO 10 is also highly stable since the PLL circuit causes the stability of the DRO output frequency f0 to track the stability of the frequency fx of the crystal oscillator 34. Hence, with the PLL circuit 32, the DRO 10 is temperature stable, or as good as the temperature stability of the crystal oscillator 34.
However, this temperature stability does not come without a price. For instance, the temperature compensated DRO circuit includes additional components, such as the crystal oscillator 34, sampling phase detector 36, loop filter 38, varactor (not shown) and directional coupler 40. These additional elements add to the costs of the DRO, increases the engineering and manufacturing time, increases inventory, complicates logistics, and reduces the reliability of the DRO circuit. Thus, there is a need for a temperature-compensated DRO that does not require such additional elements. In addition, there is a further need to provide such temperature compensation in a manner that applies to a plurality of operating frequencies so that the DROs need not be custom made.
Temperature-Compensating Resonant Frequency Tuning Device
The reason a DRO or any other dielectric resonator apparatus require temperature compensating circuitry is that the resonant frequency of a dielectric resonator can vary as a function of temperature. In more detail, the resonant frequency of a dielectric resonator is a function of its geometry and size. Typically, standard dielectric resonators available in the market are of cylindrical shape, and are often referred to as dielectric resonator pucks. Therefore, for a dielectric resonator puck, the resonant frequency is dependent on the puck""s diameter (Dr) and height (Lr). More accurately, the resonant frequency varies inversely with the puck""s diameter (Dr) and height (Lr), i.e. the larger the puck""s diameter (Dr) and height (Lr) are, the smaller the resonant frequency is, and vice-versa.
Dielectric resonators are typically comprised of temperature-expanding materials. Accordingly, as the environment temperature changes, the diameter (Dr) and height (Lr) of the dielectric resonator also change with temperature. Generally, as temperature rises, the dielectric resonator material expands, causing its diameter (Dr) and height (Lr) to increase. Conversely, as temperature drops, the dielectric resonator material contracts, causing its diameter (Dr) and height (Lr) to decrease. The resonant frequency of a dielectric resonator, on the other hand, varies inversely with the dielectric resonator size. That is, the larger the resonator""s diameter (Dr) and height (Lr) are, the smaller its resonant frequency is, and vice-versa.
It follows then that the resonant frequency of a dielectric resonator varies inversely with temperature variation. That is, as temperature rises, the resonant frequency of the dielectric resonator decreases, and as temperature drops, the resonant frequency increases. Because of the dependent relationship between the resonant frequency of a dielectric resonator and the environment temperature, achieving a desired temperature stability for dielectric resonator devices and/or circuits is not an easy task. As previously discussed, temperature compensating techniques, like the PLL technique discussed above, have been developed but are generally expensive and require sophisticated circuitry.
FIG. 3 shows a cross-sectional view of a prior art, temperature-uncompensated, dielectric resonator apparatus 50 that includes a resonant frequency tuning device 60. The dielectric resonator apparatus 50, which can include filters and dielectric resonator oscillators (DROs), consists of a metallized housing 52 configured to form an enclosed cavity 54. A dielectric resonator puck 56 mounted on a stand-off 58 is situated near the bottom of the housing 52 within the cavity 54. For resonant frequency tuning purposes, a tuning screw 60 is rotatably mounted through the top of the housing 52 and is held in secured place by a hex nut 62.
The tuning device 60 works on the principle that a metal object in proximity to a dielectric resonator affects or alters the resonant frequency of the dielectric resonator. More specifically, as a metal object approaches in proximity to a dielectric resonator, it interacts with the electromagnetic field present around the resonator, causing the resonant frequency to increase. As the metal object is removed, it interacts less with the resonator""s electromagnetic fields, causing the resonant frequency to decrease, until it is no longer affected by the metal object.
The tuning device 60 is such a metal object that can be positioned in proximity to the dielectric resonator to control or tune its resonant frequency. Typically, these prior art tuning device are configured into a threaded screw and mounted through the top of the cavity directly above the dielectric resonator 56. By rotating the tuning screw 60, the end of the screw can be positioned near the dielectric resonator to cause its resonant frequency to shift. In this manner, the screw can be positioned in order to obtain the desired resonant frequency for the dielectric resonator 60. Generally, the dielectric resonator is chosen so that its fundamental or unaffected resonant frequency is slightly lower than the desired resonant frequency. The end of the tuning screw 60 is then brought near the resonator to shift its resonant frequency up to the desired frequency.
The dielectric resonator apparatus 50 as shown in FIG. 3 does not include any temperature compensating device and/or circuits for stabilizing the resonant frequency with changes in temperature. Since the tuning screw 60 can alter the resonant frequency of the dielectric resonator, it would be highly desired if such a screw can be configured to counteract the shifts in the resonant frequency due to temperature changes. In other words, it would be highly desirable for a tuning device or screw that can be used not only for setting the desired resonant frequency of the dielectric resonator, but also to provide stability of the resonant frequency during temperature variation.
Puckless RF/Microwave Oscillator
As discussed previously, temperature compensating dielectric resonator devices and/or circuits is not an easy task. It involves substantial engineering time to properly design, manufacturing time to reliably build, and technician time to tune and test. Not only that, it requires substantially more inventory, cost and logistics for the extra components needed to provide the required temperature compensation. In other words, although these dielectric resonator devices and/or circuits achieve superior performance because of the high-Q and low loss properties, temperature compensating these devices make them not as attractive and desirable.
For instance, it would be highly desirable for an RF/Microwave oscillator that could achieve the desired performances of a dielectric resonator oscillator (DRO), such as high-Q, low-loss, and low phase noise attributes, without a dielectric resonator or a resonator that is substantially temperature dependent. Such an oscillator would not need the complicated temperature compensating techniques needed for DROs. If the temperature compensating components were to be eliminated, this would substantially reduce engineering time, manufacturing time and technician time. It would also provide substantial savings in cost because of less components, inventory and logistics. Furthermore, such an oscillator would be more reliable because of its fewer parts. Accordingly, there is a need for an RF/Microwave oscillator that achieves performances comparable to a DRO, without requiring a dielectric resonator.
The following includes some, but not all, of the objects achieved by the disclosed invention:
It is a general object of the invention to provide a new and improved dielectric resonator oscillator (DRO);
It is an object of the invention to provide a DRO that can be easily modified to optimally operate at a plurality of different discreet frequencies covering a wide frequency range;
It is another general object of the invention to provide a new and improved amplifier;
It is another object of the invention to provide an RF amplifier that can be easily modified to optimally operate at different frequency ranges;
It is another general object of the invention to provide a new and improved DC biasing or grounding circuit for an RF circuit;
It is another object of the invention to provide a DC biasing or grounding circuit that is easily tunable for a plurality of different discreet frequencies;
It is another object of the invention to provide such easily tunable DC biasing or grounding circuit for a DRO;
It is another object of the invention to provide such easily tunable DC biasing or grounding circuit for an RF amplifier;
It is another general object of the invention to provide a cavity or housing for a dielectric resonator (DR);
It is another object of the invention to provide a cavity or housing that provides improved temperature stability for a DR device;
It is another object of the invention to provide a cavity or housing that has improved temperature stability for a DR device capable of operating at a plurality of different discreet frequencies covering a wide frequency range;
It is another object of the invention to provide a cavity or housing for a DRO;
It is another object of the invention to provide a cavity or housing for a dielectric resonator filter;
It is a general object of the invention to provide an improved tuning device for tuning the resonant frequency of a dielectric resonator;
It is an object of the invention to provide a tuning device that can be easily adjusted to provide accurate tuning of the resonant frequency of a dielectric resonator;
It is another object of the invention to provide a tuning device that can substantially temperature stabilize the resonant frequency of a dielectric resonator;
It is also another object of the invention to provide a tuning device that includes multiple settings and/or adjustments so that the desired temperature stability of the resonant frequency of a dielectric resonator can be achieved;
It is another object of the invention to provide a dielectric resonator apparatus that uses the tuning device of the invention;
It is another object of the invention to provide a dielectric resonator oscillator that uses the tuning device of the invention;
It is yet another object of the invention to provide a dielectric resonator filter that uses the tuning device of the invention;
It is another general object of the invention to provide an improved RF/Microwave oscillator;
It is an object of the invention to provide an RF/Microwave oscillator that has the quality factor (Q) performance, low-loss, and phase noise characteristic comparable to a dielectric resonator oscillator; and
It is an object of the invention to provide an RF/Microwave oscillator that has the quality factor (Q) performance, low-loss, and phase noise characteristics comparable to a dielectric resonator oscillator, but with improved temperature stability.
A first aspect of the invention includes a frequency-adjustable direct current (DC) biasing or grounding circuit for any radio frequency (RF) circuit that requires a biasing or grounding circuit, such as a dielectric resonator oscillator (DRO), an RF amplifier, a mixer, a pin attenuator, and a multiplier. The advantage of having a frequency-adjustable (DC) biasing or grounding circuit is that a single design can be used for numerous RF circuits that have different frequency responses. The frequency-adjustable biasing or grounding circuit merely requires minimal tuning so that it can best operate at a desired frequency or frequency range.
The DC biasing or grounding circuit of the invention preferably includes a transmission line for propagating therethrough a direct current or a low frequency signal, and for substantially blocking or isolating an RF energy or signal cycling at a selected frequency or frequency range. The transmission line includes a first portion thereof, preferably an end (referred to herein as an RF end), for connection to an RF circuit. The transmission line includes a second portion thereof, preferably an opposite end (referred to herein as a DC end), for connection to a bias voltage, direct path to ground or a direct path to ground by way of a resistor. The electrical length between the first and second portions of the transmission line is preferably about 90 degrees or about an odd multiple thereof (i.e. 270, 450, 630 . . . Etc. degrees) for an RF energy or signal cycling at a pre-determined frequency, preferably the upper frequency in a prescribed frequency range.
The DC biasing or grounding circuit of the invention includes a low impedance structure to RF ground coupled to the transmission line at about the second portion thereof, or alternatively, the DC end of the transmission line. Because the electrical length between the first and second portions of the transmission line is about 90 degrees or about an odd multiple, the low impedance structure at the second portion (e.g. DC end) translates into a high impedance, or preferably a substantially maximized normalized impedance, at the first portion (e.g. RF end) of the transmission line for an RF energy or signal cycling at the pre-determined higher frequency.
In order to make the DC biasing or grounding circuit of the invention adjustable such that it can present a larger impedance, or preferably a substantially maximized normalized impedance, for RF energies or signals cycling at frequencies other than the pre-determined frequency, the circuit includes a tuning element coupled to the transmission line at about its first portion (e.g. RF end). Preferably, the tuning element is an open ended transmission line that has a length that can be adjusted. By adjusting the length of the open ended transmission line to a particular length, the DC biasing or grounding circuit can present a higher impedance, or preferably a substantially maximized normalized impedance, for an RF energy or signal cycling at a corresponding selected frequency.
Another aspect of the invention is an oscillator, preferably a DRO, that uses the frequency-adjustable DC biasing circuit described above to provide a bias voltage for its active device, such as a field effect transistor, bipolar junction transistor or the like. The frequency-adjustable DC biasing is particularly useful for a line of DROs producing different discrete output frequencies within a specified frequency range. The advantage of the frequency-adjustable DC biasing circuit is that a single design thereof can be incorporated into any of a number of DROs producing different discreet frequency signals.
In the preferred embodiment, the DRO includes an active device, such as a field effect transistor (FET); a dielectric resonator coupled to a port of the active device, such as the gate of the FET; and an adjustable-frequency biasing circuit for biasing the active device, such as the FET. The DRO may include impedance matching circuits as appropriate. With the frequency-adjustable DC biasing circuit, modifying the DRO for a different output frequency is simply done by adjusting the DC biasing circuit so that it provides substantially optimized RF blockage at the specified frequency, providing the proper dielectric resonator puck for the specified frequency, and performing minor tuning on the impedance matching circuits if appropriate to do so. With a versatile DC biasing circuit, a single design can be used on a plurality of different DROs. This leads to reduced costs, manufacturing and engineering efforts, inventory, logistics, and an improvement in the reliability of the DROs.
Another aspect of the invention is an improved technique for providing a gate return for a field effect transistor (FET) used in oscillators that leads to reduced phase noise. The FET gate return of the invention includes a relatively high resistor, for example of about at least 10 kilo Ohms. The resistor is connected to ground and coupled to the DRO by way of a high characteristic impedance transmission line, such that an end or portion thereof is coupled to the FET, preferably near the gate. The high impedance transmission line includes a length of about 90 electrical degrees (quarter wavelength) or about an odd multiple thereof at the operating frequency of the DRO. Preferably, the high characteristic impedance transmission line is connected to the input resonator transmission line if a series-feedback DRO is used. An RF bypass capacitor is preferably connected across the gate return resistor.
Because the FET gate resistor is of relatively high resistance, for example of about at least 10 kilo Ohms, coupled with the fact that it is further RF isolated from the DRO by the quarterwave transmission line, the DRO acquires improved phase noise performance. The FET gate return circuit of the invention can also be made frequency-adjustable, similar to the biasing or grounding circuit discussed above, such that a substantially maximized RF isolation is provided for other different output frequencies of the DRO. This leads to improved phase noise performance for the DRO at the selected frequency.
Yet another aspect of the invention is a cavity or enclosure for a dielectric resonator that provides improved temperature stability over a wide range of frequencies. This cavity would be particularly useful for a line of DROs that output different frequency signals, wherein a single cavity design could be used for all of the DROs and provide the needed temperature stability.
In particular, the dielectric resonator cavity of the invention includes a width or diameter Dc and a height Lc. It is designed to house a dielectric resonator structure, such as a dielectric resonator puck, having a width or diameter of Dr and a height Lr. According to the invention, in order to provide sufficient temperature stability, it is preferred that the diameter Dc of a cylindrical cavity be at least about 3 to about 7.5 times the width or diameter Dr of the enclosed dielectric resonator, and the height Lc of the cavity be at least about 3 to about 7.5 times the height Lr of the enclosed dielectric resonator. For a square cavity, it is preferred that the width Dc be at least about 3 to about 7.5/{square root over (2)} times the width or diameter Dr of the enclosed resonator, and the height Lc be at least about 3 to about 7.5/{square root over (2)} times the height Lr of the enclosed dielectric resonator. Since the resonant frequency of standard dielectric resonator puck linearly correlates with the diameter of the resonator, the cavity provides for improved temperature stability for a frequency range of more than an octave.
Because the dielectric resonator cavity of the invention can accommodate dielectric resonators having resonant frequencies that can differ by more than an octave, a single cavity design can be used on a line of DROs producing outputs that fall within the working frequency range of the cavity. This is of particular advantage since a single cavity design would facilitate manufacturing and engineering efforts, reduce costs, inventory and logistics, and improve the reliability of the DROs. Not only would it be useful for a line of DROs, but it would also be useful for a line of dielectric resonator filters having different frequency responses falling within the working range of the cavity. In addition, the cavity could also be used for other dielectric resonator applications.
In another aspect of the invention, a dielectric resonator tuning device is provided herein that is capable of providing substantial temperature stability to the resonant frequency of a dielectric resonator. Or, in other words, the tuning device has temperature compensation capability for substantially stabilizing the resonant frequency of a dielectric resonator as temperature varies. The temperature compensation feature of the tuning device of the invention works on the principle that as a metal object approaches a dielectric resonator, its resonant frequency tends to increase. Conversely, as a metal object is removed from the proximity of the dielectric resonator, its resonant frequency tends to decrease until it reaches its unaffected or fundamental resonant frequency.
More specifically, the tuning device can be configured such that when temperature increases, a tuning element approaches the dielectric resonator tending to cause its resonant frequency to increase. This action counteracts the tendency of the resonant frequency to decrease as the dielectric resonator expands due to the increasing temperature. Conversely, the tuning device can be configured such that when temperature decreases, a tuning element moves away from the dielectric resonator tending to cause its resonant frequency to decrease. This action counteracts the tendency of the resonant frequency to increase as the dielectric resonator contracts due to the decreasing temperature.
One of the advantages of the tuning device of the invention is that it can be configured to provide a large range of movement with temperature variation. The reason for this is that the tuning device of the invention includes at least three materials that contribute to the movement of the tuning element with temperature variations. The compositions of these materials can be chosen so that the cumulative expansion/contraction of these materials with temperature variation provides the needed movement of the tuning element to obtain the desired temperature stability of the dielectric resonator. Another advantage of the tuning device of the invention is that the individual contributions of the materials to the movement of the tuning element can be easily adjusted to precisely achieve the needed movement of the tuning element to provide the desired temperature stability of the resonant frequency of the dielectric resonator.
In more detail, the dielectric resonator tuning device is preferably comprised of a tuning element, preferably in the form of an elongated cylindrical shaft, which can be solid or hollow. The tuning element includes a portion, preferably an end of the shaft, for electromagnetically interacting with a dielectric resonator. The other end of the shaft is attached to a head portion which includes a slot for receiving a mechanical device, like a screw driver, to assist in the rotation of the tuning element. An inner sleeve is situated coaxially around the tuning element and head portion, and includes an inner set of threads configured to mate with a set of threads formed on the sides of the tuning element and on the side of the head portion. An outer sleeve is situated coaxially around the inner sleeve and includes an inner set of threads configured to mate with an outer set of threads of the inner sleeve. The outer sleeve also includes an outer set of threads for rotational attachment to a dielectric resonator housing or an additional sleeve, if needed.
The linear temperature expansion and contraction of the tuning element, the inner sleeve and the outer sleeve contribute to the overall movement of the tuning element with temperature variations. The desired range of movement of the tuning element can be achieved by proper selection of the materials for the tuning element and inner and outer sleeves. Also, the movement of the tuning element is a function of the length of the tuning element and inner and outer sleeves below their respective point of contact to their adjacent, outer element. These lengths can be changed by rotation of these elements for providing the desired movement of the tuning element.
In another aspect of the invention, an RF/Microwave oscillator is provided herein that is characterized by having high-Q, low-loss, and low phase noise performance, comparable to a dielectric resonator oscillator, with the added benefit of having a resonant circuit that is substantially invariant with changes in temperature. In the preferred embodiment, the RF/Microwave oscillator includes an active device, preferably a field effect transistor or the like, that has three terminals, such as a gate, source and drain, coupled to a tune line or resonator circuit, a feedback circuit preferably of a series type, and an output circuit, respectively. Each of these circuits comprises at least a pair of coupled transmission lines, preferably formed on a substrate in a microstrip form, and is designed to resonate substantially at the operating frequency of the oscillator.
The high-Q, low-loss, and phase noise performance of the RF/Microwave oscillator can be improved by including in the resonator, feedback and output circuits, multiple pairs of coupled transmission lines being cascaded together. The high-Q and low-loss properties of the RF/Microwave oscillator are proportional to the number of cascaded pairs of coupled transmission lines present in the resonator, feedback and output circuits. By including a sufficient amount of cascaded coupled transmission lines in these circuits, the high-Q and low-loss properties of a DRO can be achieved. The advantage of the RF/Microwave oscillator of the invention over a DRO is that its resonant structures are not substantially susceptible to variations in temperature within a given temperature range.
The RF/Microwave oscillator may also include a dc biasing circuit for biasing the active device and preventing RF leakage therethrough. The dc biasing circuit may also be configured to be frequency adjustable as previously discussed. The oscillator may also include a FET gate return circuit for removing unwanted positive charges being passed through the Schottky junction of the FET during its operation. In addition, the RF/Microwave oscillator may also include a frequency tuning circuit that is responsive to an input stimuli, such as a tuning voltage, for controlling the operating frequency of the oscillator.